Determining the crystal symmetry of epitaxial Tl-2201 thin films by X-ray diffraction

Artikel i vetenskaplig tidskrift, 2002

The crystal symmetry of epitaxial Tl-2201 films on LaAlO3 and SrTiO3 substrates is investigated by X-ray diffraction. In the case of Tl1.85Ba2CuO6 film, a φ-scan of the (1 1 10) reflection showed four diffraction peaks separated by 90.00±0.02°. A 2θ-scan of the same reflection exhibited a single peak. 2Θ−ω- and φ-scans of the corresponding reflection in Tl2.04Ba2CuO6 show splitting and broadening of the diffraction peaks indicating an orthorhombic distortion. The effect of errors in film alignment on the φ-scan and 2Θ−ω-scans is discussed. A periodic function, δ=a+bsin(ω−φ), was used to correct the φ-scan measurements. The influence of lattice mismatch between film and substrate on the structural symmetry of the films is discussed.